The invention relates to the general field of telecommunications and it relates more particularly to an architecture for an Internet protocol (IP) core network. The invention thus applies in preferred, but non-limiting, manner to communication networks complying with the long term evolution (LTE) standard defined by the third generation partnership project (3GPP) standardization consortium, and more specifically to the architecture of an LTE core network with an evolved packet core (EPC).
Exponential growth in mobile telecommunications traffic is expected in the coming years, propelled by the appearance of new applications, new terminals, and ever-faster communication data rates.
In this context, the LTE/EPC architecture has been defined by the 3GPP consortium to provide transparent IP connectivity between a user's terminal, also known as user equipment (UE), and packet data networks (PDNs) suitable for offering a variety of communication services to the terminal, such as voice over IP (VoIP) services, data downloading, video on demand, etc. This architecture relies on:                an access network known as an evolved universal terrestrial radio access network (E-UTRAN) to which the user terminal is connected via a base station known as an eNodeB (eNB); and        an IP core network (or EPC) managing data exchanges in uplink and downlink between the terminal and the data packet networks connected to the core network.        
FIG. 1 is a diagram showing the various pieces of network equipment on which the LTE/EPC architecture relies, as presently defined by the 3GPP consortium, and in particular as described in the document 3GPP TS 23.401 entitled “Technical specification group services and system aspects; general packet radio service (GPRS) enhancements for evolved universal terrestrial radio access network (E-UTRAN) access”, Release 12, March 2013. As an indication, the exchanges provided between those pieces of equipment for transferring data (i.e. in the data plane or user plane) are represented by continuous lines, whereas the signaling exchanges provided between these pieces of equipment in order to handle the data transfers (i.e. in the control or signaling plane) are represented by dashed lines.
More precisely, in FIG. 1, the EPC core network 1 enables a UE terminal 2 that is attached to (i.e. served by) an eNB base station 3A of an access network such as a mobile telecommunications network to access services made available by an external PDN 4. For this purpose, the EPC core network 1 has four types of equipment, namely:                a data transfer gateway 5, also known as a serving gateway S-GW, situated between the access network and the core network 1;        an interconnection gateway 6, also known as a PDN gateway (P-GW), for connecting the core network 1 to the external data packet network 4;        an equipment 7 for managing terminal mobility, also known as mobility management entity (MME) equipment, in charge of ensuring IP connectivity for terminals when they are in a handover situation; and        a user database 8, also known as the home subscriber server (HSS) of the network.        
The base stations 3A and 3B are directly connected to the MME equipment 7 and to the S-GW data transfer gateway 5 via respective interfaces S1-MME and S1-U.
The MME equipment 7 manages the mobility and the IP connectivity of the terminal 2 (i.e. its network connectivity). It is responsible for authenticating the terminal (in order to authorize it to access the core network 1), and it manages the setting up of communication sessions for the terminal and also intra-3GPP mobility.
The S-GW and P-GW gateways 5 and 6 are responsible for transferring data within the core network 1, for managing mobility, and for controlling quality of service in the data plane.
The MME equipment 7 is connected to the S-GW data transfer gateway 5 via a logic interface S11. The S-GW data transfer gateway 5 is connected to the P-GW interconnection gateway 6 via an interface S5.
The LTE/EPC architecture as presently defined by the 3GPP consortium is not truly optimized and it makes it difficult for operators to integrate new services in IP core networks.
More precisely, this architecture relies at present on the GPRS tunneling protocol (GTP) for managing the mobility of terminals within the network. This protocol comprises several components, including:                the GTP-U protocol that is used for transferring (exchanging) user data between two separate communication tunnels, in order to manage mobility situations of the user terminal over the interfaces S1 and S5; and        the GTP-C protocol used for setting up, updating, and maintaining the GTP communication tunnels. Signaling exchanges over the interfaces S11 and S5 rely on the GTP-C protocol.        
It should be observed that distinct GTP communication tunnels are set up for the various types of traffic that are exchanged in the network (i.e. for each quality of service), and more specifically for each packet data protocol (PDP) communication session managed by the core network. The PDP communication protocol thus contributes not only to managing terminal mobility, but also to managing the quality of service in the network.
The GTP protocol is used on top of the transport protocol implemented in the network, i.e. typically on top of the user data protocol (UDP) or possibly the transmission control protocol (TCP), which is itself executed on top of the IP protocol. Using the GTP protocol thus results in adding several headers (i.e. GTP, UDP/TCP, and IP headers) to each data packet passing through the core network, thereby significantly increasing the quantity of signaling that is exchanged between the various pieces of network equipment in order to manage the mobility of terminals and the quality of service of communications.
Furthermore, P-GW gateways for interconnecting with external packet networks and S-GW gateways for transferring data as presently provided in the LTE/EPC architecture are inflexible and generally programmed on specialized hardware. That kind of implementation provides little flexibility in terms of reusing and/or reorganizing resources.
Those two examples show up clearly the limits of the present LTE/EPC architecture concerning integrating new services.
The document by J. Kempf et al., entitled “Moving the mobile evolved packet core to the cloud”, 5th International Workshop on Selected Topics in Mobile and Wireless Computing, 2012, proposes an evolution of the LTE/EPC core network architecture defined by the 3GPP consortium in which the data and control planes are separate, and that uses the principle of software defined networking (SDN). In known manner, an SDN architecture makes it possible to decouple the control and data planes by centralizing the intelligence of the network (i.e. the control functions of the network) in a software control device. The behavior of pieces of network equipment is then defined by rules received from the control device, such as rules for processing or transferring data (i.e. traffic). The SDN concept relies on the OpenFlow™ communication protocol as defined by the open networking foundation (ONF) that enables pieces of network equipment to be programmed in simplified manner, via a standard interface.
More specifically, the document by J. Kempf et al. proposes shifting the present functions of MME equipment, and also the control plane of S-GW data transfer gateways and of the P-GW interconnection gateway to applications that execute on top of a control device implemented by a virtual machine in an external data center, also referred to as a computer “cloud”. These applications interact with the software control device via application programming interfaces (APIs). Equipment in the data plane of the transfer gateways and of the interconnection gateway, is replaced by OpenFlow™ switches; the control device is responsible for setting up the data plane.
Although that proposal simplifies the configuration of core network equipment, it nevertheless relies on the same interfaces between the control entities of the network as are defined by the 3GPP consortium and as mentioned above (i.e. the interfaces S1, S11, and S5 using the GTP protocol). The solution proposed by J. Kempf et al. thus cannot remedy the above-mentioned drawbacks in full. In particular, it does not make it possible to reduce the signaling that is induced by setting up GTP communication tunnels between the entities of the network for the purpose of improving resource management within the network and in order to enable new services to be supported by the operators of IP core networks.
Another core network architecture is proposed in the article “SoftCell: taking control of cellular core networks” by Xin Jin et al., Cornell University Library, published on May 15, 2013. That architecture comprises a controller, core switches, and distributed intermediate equipment referred to as “middleboxes”, such as firewalls, transcoders, etc. A particular function of the controller is to group together the data streams in a plurality of dimensions (i.e. policies, base stations and terminals) as aggregates of multidimensional streams that are managed by the access switches of the base stations, and it therefore needs to control the base stations directly in order to act on the aggregation of those streams. Furthermore, traffic type needs to be taken into account in order to define the middleboxes used by the data streams, in particular while they are being aggregated in the base stations, thereby making the definition of the data plane more complex, while involving limits as a result of the need to take account of this type of parameter.
This other architecture is found to be particularly complex since it makes it necessary, in the controller, to make use of user attributes and terminal attributes, and also to modify IP headers from location-dependent addresses. Unfortunately, following a handover, a terminal may need to change such a location-dependent address, and that requires old streams to be routed over an address that is different from new streams. Finally, that architecture necessarily has an impact on the base stations and the MME type radio control elements, since it is necessary for the setting up of GTP tunnels not to be controlled by an MME, unlike that which is done in the 3GPP standard.